Spinal stabilization can be achieved by providing an interbody implant. Some of these implants are bone, PEEK (polyether ether ketone), solid titanium or similar non-bone implant material and some are hollow implants that provide for inclusion of a bone graft or other suitable material to facilitate bony union of the vertebrae.
Interbody implants can be inserted into the disc space through an anterior, posterior or lateral approach. In some systems, the implants are inserted into a bore formed between adjacent vertebral bodies in the cortical endplates and can extend into the cancellous bone deep to the cortical endplates. Implant size is typically selected such that the implants force the vertebrae apart to cause tensing of the vertebral annulus and other soft tissue structures surrounding the joint space. Tensing the soft tissues surrounding the joint space results in the vertebrae exerting compressive forces on the implant to retain the implant in place.
It has been found desirable to keep the surgical opening as small as practical while still having sufficient room to insert the implant device and the end of an elongated tool or insertion instrument.
Advantageously, if the implant size could be reduced further that would allow the surgical opening to be reduced; however, once implanted the device needs to be expandable to provide sufficient spacing of the vertebrae.
A whole class of expandable interbody implant devices have been developed for this purpose. Some prior art devices use hydraulic expansion or inflatable balloons. Some devices are stackable elements piled on themselves to raise their height. Some use rotatable screw jack designs. Some are wedges that have a fixed hinged end and an opposite expandable end. Most of the rotatable expandable devices using screw threads require the device to be round cylinders or posts.
One of the problems of such devices is the amount of post insertion manipulation required to reach a fully expanded properly space height is tedious and time consuming secondly, additional set screws or locking elements are often required to keep the device at its proper size. Thirdly, the devices of a circular shape are not the best fit for the adjacent vertebrae being spaced. Fourth, most of the devices have the internal space occupied with mechanisms limiting the amount of bone growth material available for packing the implants.
The wedge type implants generally contact the bone on an angle and expandable wedges when expanded simply expand on an angle not parallel to the vertebrae surface. This places localized high loading between the vertebrae because the wedge surfaces are not parallel to the vertebrae.
In some cases of vertebral misalignment, a controlled angulation of the implant device can be very beneficial to correct a pre-existing condition. Accordingly, in those cases having a wedge shape at a fixed angulation would mean the manufacturer would be required to make many devices with pre-set angles to select from. This simply is cost prohibitive.
Previous ramped methods of expansion limit the range of expansion height, and therefore maximum angle, of the implant by using ramped surfaces directly onto the base plate which contacts the endplate of the vertebral body. Other expansion methods include cylindrical gear drive features, hinged linkages, and cams/ramps forcing base plate(s) apart through plastic deformation of the material. The cylindrical gear drive features limit the amount of bone graft space available within the interbody cage to promote fusion, unsupported hinged linkages reduce load bearing surface area and negatively affect the expansion strength and overall strength of the interbody cage. Other devices use material deformation which limits the amount of expansion capability and reduces the structural integrity of the interbody cage. The present invention overcomes all these deficiencies.
The present invention provides a device that can be expanded angularly to allow the surgeon to choose the ideal lordotic angle he wants to use to correct the spinal alignment.
These and other limitations in the prior art have been corrected and solved by the present invention as disclosed herein.